nospec.h File Reference

#include <linux/kernel.h>

Include dependency graph for nospec.h:

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Macros
#define	array_index_nospec(index, size)

Macro Definition Documentation

array_index_nospec

#define array_index_nospec	(		index,
			size
	)

Value:

({                                  \
    typeof(index) _i = (index);                 \
    typeof(size) _s = (size);                   \
    /* see header: _i must fit an unsigned long; _s may be size_t */    \
    BUILD_BUG_ON(sizeof(_i) > sizeof(unsigned long));       \
    unsigned long _mask =                       \
        array_index_mask_nospec((unsigned long)_i,      \
                    (unsigned long)_s);     \
    (typeof(_i))(_i & _mask);                   \
})

array_index_nospec - sanitize an array index after a bounds check

For a sequence like:

if (index < size) {
    index = array_index_nospec(index, size);
    val = array[index];
}

if the CPU speculates past the bounds check this clamps the index into [0, size). Used by virtio-rng.c's copy_data() to keep a buggy or malicious virtio-rng backend from steering the memcpy past the end of vi->data.